Hard disk drives that are used in mobile computers have to be designed to withstand the rough usage typically seen in the mobile environment. The shock robustness of such drives has improved primarily in the ability to withstand large shocks during the nonoperating mode. Unfortunately, the ability of these drives to withstand rough handling during operation has not seen similar gains. Indeed, the operating shock specifications have typically lagged behind non-operational specifications by about a factor of four.
As a consequence, it is not unusual for a drive in a mobile environment to be rather easily damaged during use. Damage typically is non-catastrophic but results in the loss of data. As recognized herein, this damage by a lower magnitude shock event during operating conditions occurs by a slider-to-disk contact resulting from a disturbance in the air bearing due to the shock forces. Such an event is usually not accompanied by irreversible mechanical damage. However, for higher magnitude shock events, other mechanical components can start touching each other and this eventually can result in much more severe damage.
The present invention understands that the forces from the shock event will cause the mechanical components of the drive to vibrate and thereby may cause the suspension to start flapping up and down. The slider at first is not highly likely to contact the disk when the suspension moves down toward the disk because the slider is capable of withstanding significant forces that act normal towards the disk surface due to the restoring air bearing pressure beneath the slider, which increases exponentially as the slider is forced closer to the disk surface. However, when the suspension moves away from the disk, the preload it applies on the slider will be decreased proportionately. At some level of movement the preload will be overcome and the suspension will then attempt to pull the slider away from the disk surface. At some point it can be anticipated that the air bearing will be disrupted and the slider lifted off the disk. Subsequently when the suspension whips the head back towards the disk a few milliseconds later, the slider orientation is not likely to be optimally positioned to generate the air bearing instantly and so prevent a corner of the slider from touching the disk. This is when the slider-disk contact will occur.
As further recognized herein, many sliders use a negative pressure air bearing design in which pockets in the air bearing surface generate a vacuum that pulls the slider down towards the disk surface. The stable fly height of these sliders is the position where the suspension pre-load and this downward vacuum pull is balanced by the upward acting pressure under the air bearing portion of the slider. Having made the above critical observations, the present invention is provided.